1. Field of the Invention
The invention relates to a centreless cylindrical grinding machine for through-feed and in-feed grinding of various workpieces. Instead of the terms through-feed and in-feed grinding other terms such as longitudinal grinding and traverse grinding are also used in the literature.
2. Description to Related Art
Centreless cylindrical grinding machines differ from the usual cylindrical grinding methods in that the workpiece to be processed is not clamped positively in the machine or a device, but rests loosely on a support (workpiece support). Centreless grinding enables higher manufacturing precision and higher productivity compared to other cylindrical grinding methods.
Current construction of centreless cylindrical grinding machines usually have a grinding spindle head driven in an axis (XS) with a grinding wheel a well as a regulating wheel spindle head with a regulating wheel likewise driven in an axis (XR). Fixed solidly on the machine bed between both spindle heads is the workpiece support or a bearing block serving the same purpose. Wheel-truing attachments for the grinding wheel and the regulating wheel are as a rule attached externally and can be moved by other driven axes (X′ and Y′ as well as X″ and Y″) relative to the respective spindle heads. The drawback to this construction is that there is a large number—as many as six!—of driven positioning axes, making these machines considerably more expensive.
EP-0 674 970 describes a centreless cylindrical grinding machine, in particular used for manufacturing valve rods and the like. The machine is operated in through-feed mode, since the regulating wheel is slightly inclined compared to the grinding wheel. The machine has a fixed workpiece support in the form of a plate with an angled bearing surface as well as motor-adjustable limit stops for positioning the workpiece arranged on both sides. The limit stops can be positioned in a direction parallel to the rotating axis of the grinding wheel. The workpiece support and the grinding spindle head and the regulating spindle head are not located inside a safety housing. Since the workpiece support is arranged fixed, there is also no possibility of moving the workpiece support for the purpose of operating from the danger zone of the grinding and regulating wheel.
GB-2 206 299 describes a centreless cylindrical grinding machine in which two workpiece supports are arranged on a shuttle which in turn glides on a carriage track. The carriage is not driven, but can be moved for loading the workpieces or for unloading same on one or the other side, such that at least one of the workpiece supports comes to rest fully beyond the processing zone between the grinding and the regulating wheel. The carriage with the workpiece support serves only to pick up the workpieces, carries no wheel-truing attachments and structurally is not designed to pick up wheel-truing attachments. The grinding and the regulating wheel are arranged in a work station and there are also several partial regulating wheels present. The partial regulating wheels seem to always come into use at the same time.
DE 1 994 0687 describes in FIG. 8 a grinding machine for centreless grinding of workpieces with a carriage, located on which is a workpiece support and to which dressers are also fastened. The carriage is driven and (again with the aid of the abovementioned axis directions) and can be moved in Y direction, while the grinding and the regulating wheel can be moved in XS or XR direction respectively. Through this arrangement the number of driven positioning axes is reduced, without any loss in functionality as compared to 4-axis or even 6-axis driven machines. Furthermore, with this machine type the rotating axis of the grinding wheel is set obliquely to a longitudinal central axis running in Y direction.
In this machine type the workpiece support is moved into a position next to the grinding and the regulating wheel during a truing procedure, but even then remains in the immediate vicinity of same and there are no separating or safety means which reliably protect the operator from accidental contact with the grinding wheel or the regulating wheel while a workpiece is being changed. The workpiece support can thus not be fully removed for operating from the danger zone of grinding wheel and regulating wheel. The dressers attached to the carriage in this machine can only be used in an inner-acting manner (inner-acting here means that they are put to use in the region of the workpiece support, thus essentially between the grinding and the regulating wheel). With regard to protection and accessibility during change of dressers essentially the same disadvantages arise as during exchange of workpieces.
More recent machines are often fully contained, thus guaranteeing a high level of safety. One of the manufacturers for example is the firm SCHAUDT MIKROSA BWF in Leipzig, with the machine type KRONOS S. The firm DOUGLAS CURTIS LTD in Colchester, Essex is manufacturer of another centreless cylindrical grinding machine of more recent construction of the type CURTIS UCG [Universal Centerless Grinder]. Information on both firms and machine types can be accessed via the Internet. With the abovementioned machines the moving parts are always arranged completely inside a full housing.